Performance of recycled aggregate concrete-filled high-strength steel tubular members under combined compression-bending-torsion

This paper presents an investigation into the behaviour of recycled aggregate concrete-filled high-strength steel tubular (RAC-FHST) members subjected to combined compression-bending-torsion. A series of 32 RAC-FHST specimens were tested under combined compression-torsion, bending-torsion and compression-bending-torsion loading states. The primary parameters varied in the tests included the yield strength of steel tube, the axial load ratio and the bending moment level. A comprehensive analysis was conducted on the typical failure modes, full-range torsional moment-rotation response, and ultimate strength of the specimens. The results indicated that the mechanical behaviour of RAC-FHST members was enhanced owing to the superior confinement effect provided by the steel tube. A finite element modeling approach is developed and validated to examine the mechanical behaviour, failure modes, and the influence of the confinement factor on the normalized axial force-bending moment-torsion ( N / N u - M / M u - T / T u ) interaction curves. Based on the analysis, simplified calculation methods are proposed for predicting the ultimate strength of RAC-FHST members under combined compression-bending-torsion. These simplified calculation methods offer valuable references for engineering applications . • A set of experimental data on RAC-FHST members under combined compression-bending-torsion is presented. • An FE model is developed and verified against the experimental results. • Internal force distribution and stress state are analyzed. • An existing method for predicting the torsional resistance of RAC-FHST members is evaluated.